1. Technical Field
The present invention relates to a liquid discharging apparatus. More specifically, the present invention relates to a controller and a method of controlling the discharging apparatus.
2. Related Art
An ink jet printer is one example of a liquid discharging apparatus currently known in the art. Typically, ink jet printers perform a printing process by discharging a liquid ink from a plurality of nozzles of a head onto various types of medium, such as paper, cloth, or film.
Unfortunately, however, when the openings of the nozzles are exposed to the atmosphere, there is a possibility that moisture, which acts as a solvent of the ink, may evaporate at the distal end portions of the nozzles where the ink is exposed to the external air. As the ink evaporates, the ratio of dissolved matter, such as dye, or the ratio of solid matter, such as pigment, to the solvent of the ink may increases over time and, as a result, the ink present at the distal end portions of the nozzles may become thickened, with an increased viscosity. This thickening not only adversely affects the amount of ink discharged and the positions at which ink lands but also causes clogs in the nozzles when the ink becomes too thick.
For this reason, when a printing process is not performed in a relatively long period of time, such as when the printer is in a power OFF state or in a print standby state, the nozzle forming face of the head, where the nozzles are formed, is covered with a cap member in order to prevent thickening around ink surfaces.
In some instances, such as in the Japanese Patent No. JP-A-2004-230832, the cap member may have a substantially rectangular-parallelepiped-box shape, where one wall of the box that faces the head is removed. Then, when the cap member is pressed against the head, the four sides of the cap member are brought into contact with the nozzle forming face in order to form a gap between the cap member and the distal end edges of the nozzles. Thus, the nozzles are covered and shielded against the surrounding space.
In recent years, in order to reduce printing time, line head printers have been developed, wherein the recording head has a length that is equal to or greater than the width of the printing medium with a nozzle column of aligned nozzles formed thereon. During a printing process using the line head printer, the recording head is able to print an image on a medium which is transported in a printing direction relative to the recording head, while the recording head remains in a fixed position. In this manner, high-speed printing may be achieved.
In the case of the line head printer, because the overall length of the nozzle column of the head is long, it is also necessary to increase the overall length of the cap member that covers the nozzle column. One problem with this configuration, however, is that there are many technical problems, such as squashed nozzles, that need to be addressed in order to form the above described box-shaped cap member of a sufficient length. In addition, in order to elongate the nozzle column of the head, a plurality of head units are connected to form one head. In this case, there will be a step between the connecting portions of the head units, making it difficult to bring the cap member into close contact with the head.
In some situations, instead of using a box-shaped cap member, the openings of the nozzles are closed using a flat plate member, which has a shape that is simpler than the cap members currently known in the art, that is, the cap member operates by simply bringing the flat face of the flat plate member into close contact with the nozzle forming face. Furthermore, there is a need for a configuration that can work even when the cap member is not firmly brought into close contact with the head.
However, as the flat face of the flat plate member is brought into close contact with the nozzle forming face, because the liquid level of ink is positioned adjacent to the nozzle openings, there is a possibility that, when the flat plate member closely contacts the nozzle forming face, the flat face of the flat plate member may contact the ink and thereby break the menisci of ink. In addition, when the cap member does not closely contact the head, there has been a problem that ink in the nozzles of the head dries and then thickens.